Variable Interest Entities - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Variable Interest Entity
Assets	$ 201,996		$ 201,996		$ 169,369
Lower limit
Variable Interest Entity
Unfunded commitments, year expected to be funded			2020
Upper limit
Variable Interest Entity
Unfunded commitments, year expected to be funded			2036
Variable Interest Entity, Primary Beneficiary | Automobile loan
Variable Interest Entity
Carry value of automobile loans securitized					1,430
Face amount of notes issued or redeemed					1,370
Long-term debt retained					68
Assets	944		$ 944		1,429
Variable Interest Entity, Not Primary Beneficiary | Loans provided to VIEs
Variable Interest Entity
Unfunded commitment amounts			1,300		1,400
Variable Interest Entity, Not Primary Beneficiary | CDC investments
Variable Interest Entity
Assets	1,473		1,473		1,435
Variable Interest Entity, Not Primary Beneficiary | CDC investments | Qualified Affordable Housing Tax Credits
Variable Interest Entity
Assets	1,200		1,200		1,200
Unfunded commitments in qualifying LIHTC investments	436		436		428
Variable Interest Entity, Not Primary Beneficiary | Private equity investments
Variable Interest Entity
Assets	96		96		89
Unfunded commitment amounts			86		$ 75
Capital contribution to private equity investments	$ 4	$ 2	$ 10	$ 9